Marinette County, Wis., District Attorney Brent DeBord has yet to file formal charges against Scott J. Johnson of Kingsford, Mich. But in a letter sent to the state Justice Department asking for help prosecuting the case, DeBord said he expects Johnson to enter a not guilty by reason of mental defect plea, Bill Cosh, spokesman for the Wisconsin Department of Justice, said Tuesday.

The letter doesn't elaborate on why DeBord anticipates that plea, and the district attorney didn't return messages Tuesday afternoon.

Police believe Johnson, 38, emerged from the woods near Niagara on the Menominee River, which forms Wisconsin's border with Michigan's Upper Peninsula, on Thursday and gunned down Tiffany Pohlson, 17, of Vulcan, Mich., and Anthony Spigarelli, 18 and Bryan Mort, 19, both of Iron Mountain.

A fourth victim, Daniel "Bud" Gordon, 20, of Kingsford, suffered a superficial injury. Emergency workers treated him at the scene for a shrapnel wound in his back, said Scott Celello, the undersheriff in Dickinson County, Mich.

Johnson surrendered on Friday morning after teams of police spent the night combing the woods for him.

Pohlson's funeral was held Tuesday afternoon. Spigarelli's was scheduled for the evening. Services for Mort are scheduled for Thursday in Iron Mountain.

Johnson, an Army veteran who never served overseas, appears to have used a military-type assault rifle, Sauve said. Investigators may never know how many shots were fired at the river, he said, but the Marinette County coroner has said Pohlson and Spigarelli were killed by single gunshot wounds to the head.

Results for Mort's autopsy, which is being done in Michigan, have not yet been released. Pohlson and Spigarelli were killed at close range -- about 20 feet from the shooter on the Wisconsin side of the river, Sauve said. Mort was on the Michigan riverbank 80 to 100 yards away when he was shot, he said.

"It takes some marksmanship to make that kind of shot," Sauve said.

The three who were killed and Gordon were fleeing as the shots were fired, Celello said. All the shots came from the Wisconsin side of the river.

Marinette County authorities did not know whether Johnson had a lawyer. Johnson's mother, Judy Johnson, said her son had no money and would likely require a court-appointed public defender.

Messages left at the state public defender offices in Peshtigo and Green Bay weren't returned.

It's unclear when charges might come against Johnson. Marinette County Chief Deputy Jerry Sauve said the investigation could take several more weeks as detectives are still interviewing witnesses and compiling reports.

DeBord told Attorney General J.B. Van Hollen in his letter he needs help because his half-time assistant left to take a full-time job in Kenosha County and he's trying to handle another homicide that took place July 26 in the city of Marinette.

Assistant Attorney General Roy Korte wrote back to DeBord on Tuesday and told him Assistant Attorney General Gary Freyburg would help him. DeBord will remain the lead prosecutor on the case.